Studies are planned on the formation, metabolism and disposition of bilirubin in the liver of experimental animals, in isolated perfused rat liver, and in hepatocyte monolayer culture. These will be complemented by investigations of the synthesis, turnover, and degradation of heme and hemoproteins. Specifically, attempts will be made to characterize the compartmental arrangement and the turnover rate of the various hemoproteins that are potential sources of bilirubin formation in the hepatocyte. In addition, the enzymatic mechanism will be studied by which heme is converted in the liver to bilirubin with the specific aim of isolating and characterizing the microsomal protein moiety of heme oxygenase. Experiments will be performed to obtain conclusive quantitative information on the role of microsomal heme oxygenase in the conversion of heme to bilirubin in vivo. Since biliverdin is an intermediate in this reaction, its physiological and potential cytotoxic properties will be examined in intact animals and in hepatocytes in tissue culture. Specifically, bilirubin and biliverdin will be compared with regard to their transplacental transfer from fetus to mother. Finally, detailed investigations in vitro and in vivo will be performed to test the hypothesis that bile acids and other bile constituents in the bile canaliculi serve as a micellar sink for excretion of conjugated bilirubin and other organic anions by the liver cell. Individually and collectively these studies are expected to provide new and additional information in specific areas of liver function that presently are poorly understood.